The present invention relates to a technique monitoring a characteristic such as a current value of an electron beam.
For prior art electron beam monitoring, a Faraday cup having a large hole of about several millimeters provided on a stage is used.
In this case, to efficiently absorb an incident electron beam, as the material of the Faraday cup, a relatively light metal having a small back scattering coefficient or a silicon (Si) substrate as described in Japanese Patent Application Laid-Open No. 3-48190 is optimal.
In order to achieve high-throughput of an electron beam writing system, a multi-beam writing system (multi-electron beam writing system) performing writing or monitoring using multiple beams at the same time is required. In such multi-beam writing system, micro electron beams are arrayed in a small region at high density. In order that they each pass through an electron optical system, beam monitoring must be performed for each of the beams. It takes time to monitor such multiple beams one by one using one Faraday cup.
Japanese Patent Application Laid-Open No. 11-176365 shows a system in which a plurality of lens tubes and Faraday cups opposed thereto are arranged. The prior art micro Faraday cups of a relatively light metal or a silicon substrate arranged at high density are used. Most of an incident electron beam passes through the Faraday cups. Precise monitoring cannot be done.
Japanese Patent Application Laid-Open No. 8-179046 shows an example using Faraday cups of gold (Au) for ion beam monitoring. This copes with charging due to oxidation when an oxygen ion beam is irradiated. Gold is used as an inactive material.
An object of the present invention is to provide a beam monitoring sensor which can offer both high beam monitoring precision and high speed monitoring in a multi-electron beam writing system and a monitoring method using the same.
To solve the above problems, in the present invention, as the member of an electron beam collecting part forming Faraday cups monitoring an electron beam characteristic, tantalum (Ta), a heavy metal having an atomic number larger than that of Ta (for example, W (tungsten), Au and so on), or a compound having them as a main constituent is used.
In this case, the number of back scattered electrons from the bottom surface of the Faraday cup is increased. When the Faraday cup has a deep hole having an aspect ratio above 4, a micro Faraday cup having a good absorbing efficiency is enabled. When the Faraday cup hole size is small toward its top, the back scattered electrons can be confined more reliability. Precise monitoring can be realized.
A plurality of such Faraday cups are arranged at high density to respond to multiple beams. The pitch of the Faraday cup array is the same as that of the array of electron beams monitored or an integral multiple thereof. The multiple beams can be monitored precisely at the same time. In this case, the minimum value of the pitch of the Faraday cup array depends on the acceleration voltage of the electron beam monitored and the material element. When it is larger than the pitch of the electron beam array, only the beam opposed to the Faraday cup array is turned on for monitoring. The unmonitored beam is monitored whenever necessary by beam deflection or stage movement corresponding to the Faraday cup array. A high speed process is enabled.
When the Faraday cup array is required to be denser so as not to prevent beam transmission completely, a leak ratio from the Faraday cup is obtained. A contribution of the adjacent Faraday cup to a monitored value is assumed. A beam current can be monitored by a value obtained by the addition of an absorbed current of the irradiated Faraday cup and the contribution to a current value of the adjacent Faraday cup. Otherwise, an electrode layer is provided on the underlayer of the Faraday cup to apply a negative voltage thereto, producing a negative acceleration in the incident electron. Leak from the Faraday cup can be thus prevented. This permits precise current value monitoring of an electron beam incident upon the respective Faraday cups.
Representative construction examples of the present invention will be shown below.
(1) An electron beam monitoring sensor, which has a Faraday cup having an electron beam collecting part for monitoring an electron beam characteristic and forms the member of the electron beam collecting part by tantalum, a heavy metal having an atomic number larger than that of tantalum, or a compound having at least one of the heavy metals as a main constituent.
(2) The electron beam monitoring sensor, wherein the electron beam collecting part is of a recess shape having a hole, the thickness of the bottom surface and the side wall of the recess shape is larger than a range of an electron beam monitored, and the depth of the recess shape is above four times the size of the hole.
(3) The electron beam monitoring sensor, wherein the size of the hole of the recess shape is small toward its top.
(4) The electron beam monitoring sensor, wherein the member of the electron beam collecting part is formed by any one of heavy metals including tantalum, tungsten and gold.
(5) The electron beam monitoring sensor, wherein a plurality of the Faraday cups are arrayed at a predetermined pitch in two dimensions corresponding to multiple electron beams.
(6) The electron beam monitoring sensor, wherein the array pitch of the Faraday cups is larger than twice the range of the electron beam of the electron beam collecting part, and is the same as the pitch of multiple electron beams monitored or an integral multiple thereof.
(7) The electron beam monitoring sensor, wherein the plurality of Faraday cups are formed on the same substrate having a dielectric layer inserted therein.
(8) The electron beam monitoring sensor, wherein the plurality of Faraday cups are each connected to an ammeter for monitoring an electric current of an electron beam by each wire, and the wires are formed by a multi layer structure in the substrate.
(9) An electron beam monitoring method, which has the step of irradiating multiple electron beams onto a plurality of Faraday cups arranged in two dimensions at an array pitch of an integral multiple of the beam pitch of the multiple electron beams and formed by tantalum or a heavy metal having an atomic number larger than that of tantalum so as to monitor a beam current of each of the electron beams, and stops irradiation of the electron beam of the multiple electron beams not opposed to the Faraday cup to selectively irradiate only the electron beam opposed to the Faraday cup onto the Faraday cup, thereby monitoring the beam current by an absorbed beam current of each of the Faraday cups.
(10) An electron beam monitoring method, which has the step of irradiating multiple electron beams onto a plurality of Faraday cups arranged in two dimensions at an array pitch of an integral multiple of the beam pitch of the multiple electron beams and formed by tantalum or a heavy metal having an atomic number larger than that of tantalum so as to monitor a beam current of each of the electron beams, and monitors the each beam current by the addition of an absorbed beam current of a first Faraday cup of the plurality of Faraday cups onto which the electron beam is irradiated and part of an absorbed beam current of a second Faraday cup adjacent to the first Faraday cup.
(11) The electron beam monitoring method, wherein while applying a negative voltage to the Faraday cup, an electron beam is irradiated onto the position opposed to the Faraday cup.